Delivering organic powder to a vaporization zone

ABSTRACT

A method for vaporizing organic materials and condensing them onto a surface to form a layer, comprising: providing a quantity of organic material in a powdered form in a first container; fluidizing the organic material in the first container and transferring such fluidized material to an auger structure; and rotating at least a portion of the auger structure to transfer fluidized powder from the first container along a feeding path to a vaporization zone where such powder is vaporized and delivered to the substrate to form the layer.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. patent application Ser. No.10/805,980 filed Mar. 22, 2004 entitled “Vaporizing Fluidized OrganicMaterials” by Long et al., U.S. patent application Ser. No. 10/784,585filed Feb. 23, 2004, entitled “Device and Method for VaporizingTemperature Sensitive Materials” by Long et al. and U.S. Publication No.2006/0062919, entitled “Delivering Organic Powder to a VaporizationZone” by Long et al, the disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the field of physical vapor depositionof organic powder.

BACKGROUND OF THE INVENTION

An OLED device includes a substrate, an anode, a hole-transporting layermade of an organic compound, an organic luminescent layer with suitabledopants, an organic electron-transporting layer, and a cathode. OLEDdevices are attractive because of their low driving voltage, highluminance, wide-angle viewing and capability for full-color flatemission displays. Tang et al. described this multilayer OLED device intheir U.S. Pat. Nos. 4,769,292 and 4,885,211.

Physical vapor deposition in a vacuum environment is the principal meansof depositing thin organic material films as used in small molecule OLEDdevices. Such methods are well known, for example Barr in U.S. Pat. No.2,447,789 and Tanabe et al. in EP 0 982 411. The organic materials usedin the manufacture of OLED devices are often subject to degradation whenmaintained at or near the desired rate dependant vaporizationtemperature for extended periods of time. Exposure of sensitive organicmaterials to higher temperatures can cause changes in the structure ofthe molecules and associated changes in material properties.

To overcome the thermal sensitivity of these materials, only smallquantities of organic materials have been loaded in sources and they areheated as little as possible. In this manner, the material is consumedbefore it has reached the temperature exposure threshold to causesignificant degradation. The limitations with this practice are that theavailable vaporization rate is very low due to the limitation on heatertemperature, and the operation time of the source is very short due tothe small quantity of material present in the source. In the prior art,it has been necessary to vent the deposition chamber, disassemble andclean the vapor source, refill the source, reestablish vacuum in thedeposition chamber and degas the just-introduced organic material overseveral hours before resuming operation. The low deposition rate and thefrequent and time consuming process associated with recharging a sourcehas placed substantial limitations on the throughput of OLEDmanufacturing facilities.

A secondary consequence of heating the entire organic material charge toroughly the same temperature is that it is impractical to mix additionalorganic materials, such as dopants, with a host material unless thevaporization behavior and vapor pressure of the dopant is very close tothat of the host material. This is generally not the case and as aresult, prior art devices frequently require the use of separate sourcesto co-deposit host and dopant materials.

A consequence of using single component sources is that many sources arerequired in order to produce films containing a host and multipledopants. These sources are arrayed one next to the other with the outersources angled toward the center to approximate a co-depositioncondition. In practice, the number of linear sources used to co-depositdifferent materials has been limited to three. This restriction hasimposed a substantial limitation on the architecture of OLED devices,increases the necessary size and cost of the vacuum deposition chamberand decreases the reliability of the system.

Additionally, the use of separate sources creates a gradient effect inthe deposited film where the material in the source closest to theadvancing substrate is over represented in the initial film immediatelyadjacent the substrate while the material in the last source is overrepresented in the final film surface. This gradient co-deposition isunavoidable in prior art sources where a single material is vaporizedfrom each of multiple sources. The gradient in the deposited film isespecially evident when the contribution of either of the end sources ismore than a few percent of the central source, such as when a co-host isused. FIG. 1 shows a cross-sectional view of such a prior-artvaporization device 5, which includes three individual sources 6, 7, and8 for vaporizing organic material. Vapor plume 9 is preferablyhomogeneous in the materials from the different sources, but in factvaries in composition from side to side resulting in a non-homogeneouscoating on substrate 15.

A further limitation of prior art sources is that the geometry of thevapor manifold changes as the organic material charge is consumed. Thischange requires that the heater temperature change to maintain aconstant vaporization rate and it is observed that the overall plumeshape of the vapor exiting the orifices can change as a function of theorganic material thickness and distribution in the source, particularlywhen the conductance to vapor flow in the source with a full charge ofmaterial is low enough to sustain pressure gradients from non-uniformvaporization within the source. In this case, as the material charge isconsumed, the conductance increases and the pressure distribution andhence overall plume shape improve.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an effective way oftransferring organic powder from a container to a vaporization zone.

This object is achieved by a method for vaporizing organic materials andcondensing them onto a surface to form a layer, comprising:

(a) providing a quantity of organic material in a powdered form in afirst container;

(b) fluidizing the organic material and transferring such fluidizedmaterial to an auger structure; and

(c) rotating at least a portion of the auger structure to transferpowder from the first container along a feeding path to a vaporizationzone where such powder is vaporized and delivered to the substrate toform the layer.

It is an advantage of the present invention that the continuous heatingof material during operation of prior art devices is eliminated in thatonly a small portion of organic material is heated, for a short periodof time and at a controlled rate. The bulk of organic material ismaintained at a temperature that can be as much as 300° C. cooler thanthe desired rate-dependant vaporization temperature.

It is a further advantage of the present invention that it can maintaina steady vaporization rate with a continuously replenished charge oforganic material and with a steady heater temperature. The device thusallows extended operation of the source with substantially reduced riskof degrading even very temperature-sensitive organic materials.

It is a further advantage of the present invention that it permitsmaterials having different vaporization rates and degradationtemperature thresholds to be co-sublimated in the same source.

It is a further advantage of the present invention that it permitslinear vaporization rate control by controlling the volumetric meteringrate or controlling the feed pressure of the compacted organic materialpowder.

It is a further advantage of the present invention that it can rapidlystop and reinitiate vaporization and achieve a steady vaporization ratequickly by controlling the metering rate of the organic material,minimizing contamination of the deposition chamber walls and conservingthe organic materials when a substrate is not being coated.

It is a further advantage that the present device achieves substantiallyhigher vaporization rates than in prior art devices with substantiallyreduced material degradation. Further still, no heater temperaturechange is required as the source material is consumed.

It is a further advantage of the present invention that it can provide avapor source in any orientation, which is frequently not possible withprior-art devices.

It is a further advantage of some embodiments of this invention that itcan remove adsorbed gases from the organic powder through the use ofheat and vacuum as a much smaller quantity of powder is conveyed throughthe device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior-art vaporization device;

FIG. 2 is a three-dimensional view of one embodiment of an apparatusaccording to the present invention for vaporizing organic materials andcondensing them onto a surface to form a layer;

FIG. 3 is a cross-sectional view of one embodiment of a portion of theabove apparatus for feeding powder according to the present invention,including one embodiment of an agitating device useful in the presentinvention;

FIG. 4 is a cross-sectional view of one embodiment of a portion of theabove apparatus for feeding and vaporizing powder according to thepresent invention;

FIG. 5 shows a graphical representation of vapor pressure vs.temperature for two organic materials;

FIG. 6 a is a cross-sectional view showing one embodiment of an augerstructure useful in this invention;

FIG. 6 b is a cross-sectional view of the terminal end of the augerstructure in FIG. 6 a;

FIG. 6 c is a relief view showing another embodiment of an augerstructure useful in this invention;

FIG. 6 d is a cross-sectional view showing another embodiment of anauger structure useful in this invention;

FIG. 7 is a cutaway view of another embodiment of an agitating deviceuseful in the present invention;

FIG. 8 is a cutaway view of another embodiment of an agitating deviceuseful in the present invention;

FIG. 9 is a three-dimensional view of a portion of another embodiment ofan apparatus according to the present invention for vaporizing organicmaterials and condensing them onto a surface to form a layer, includingan apparatus to drive off adsorbed gasses or impurities;

FIG. 10 is a cross-sectional view of a device according to the presentinvention including a deposition chamber enclosing a substrate; and

FIG. 11 is a cross-sectional view of an OLED device structure that canbe prepared with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to FIG. 2, there is shown a three-dimensional view of oneembodiment of an apparatus according to the present invention forvaporizing organic materials and condensing them onto a surface to forma layer. Vaporization apparatus 10 includes manifold 20 and attachedfeeding apparatus 40. Feeding apparatus 40 includes at least firstcontainer 50 and feeding path 60, and can also include second container70. First container 50 is provided with a quantity of organic materialin a powdered form. Second container 70 can receive the organic materialand transfer it to first container 50 as will become evident. Manifold20 includes one or more apertures 30 through which vaporized organicmaterial can exit to a substrate surface. Manifold 20 is shown in anorientation whereby it can form a layer on a vertically-orientedsubstrate, but it is not limited to this orientation. Manifold 20 can beoriented horizontally and can form a layer on a horizontal substrate.Manifold 20 had been described in detail by Long et al. incommonly-assigned, above-cited U.S. patent application Ser. No.10/784,585. Feeding apparatus 40 is shown attached to the bottom ofmanifold 20, that is, opposite to apertures 30, but feeding apparatus 40can also be attached to a side of manifold 20. The nature of theattachment of feeding apparatus 40 to manifold 20 will become clear.

Turning now to FIG. 3, there is shown a cross-sectional view of oneembodiment of a portion of the above vaporization apparatus for feedingpowder according to the present invention whereby organic material isfluidized and transferred to the auger structure. First container 50holds organic material 160, which is in the form of a finely dividedpowder and is desirably of a uniform size, and which feeds into augerstructure 80 in feeding path 60. Auger structure 80 passes through theinterior of first container 50 and feeds into the manifold describedabove (not shown for clarity). At least a portion of auger structure 80is rotated by motor 90 so as to transfer the organic material powder ata controlled volumetric rate or pressure along feeding path 60 to avaporization zone where the organic material powder is vaporized andsubsequently delivered to a substrate to form a layer. Feeding path 60,and therefore organic material powder in feeding path 60, can bemaintained at a temperature below the desired vaporization temperatureof the organic material. To facilitate the movement of organic material160 to auger structure 80, organic material 160 is fluidized byagitating organic material 160 by using an agitating device, e.g.piezoelectric structure 130 or an electromechanical vibrator. Suchfluidized material is more readily transferred to auger structure 80 bygravity feed.

The addition of optional second container 70 to hold additional organicmaterial 100 provides several additional advantages. A large quantity oforganic material 100 can be charged in the apparatus, allowingcontinuous operation of the device for extended periods of time. Bysensing the quantity of organic material in first container 50, e.g. bymeasuring the height of the column of organic material 160, one canselectively meter the amount of organic material powder transferred fromsecond container 70 to first container 50 and provide a substantiallyconstant volume of organic material 160 in first container 50, e.g. ±5cm³. In practice, 10 cm³ of powder is loaded in first container 50. Someembodiments described herein have great process latitude with respect toreliable powder feeding over a wide range of powder height in thecontainer and can be run nearly to exhaustion without failing to feedpowder. However, it is believed that multi-component mixing homogeneityis fostered if an optimum powder height is established and maintained infirst container 50 to within ±10%. This minimizes variations in thefeeding rate of organic material 160 to feeding path 60. Also, secondcontainer 70 can be arranged to be refillable without affecting theoperation of first container 50, allowing the device to be continuouslyoperated for even longer periods of time. Organic material 100 ismaintained in second container 70 by e.g. screens 110 and 120, whosemesh size is chosen to prevent the free flow of powdered material.Screens 110 and 120 can also be the mechanism for providing measuredquantities of organic material to move from second container 70 to firstcontainer 50. Screens 110 and 120 are contacted by agitating devices(not shown) that can be actuated to cause a quantity of powder to passthrough the screen. Such devices include those to vibrate the screen, ora movable arm immediately above or below the screen to allow selectiveagitation of screens 110 and 120. A commercial flour sifter is one suchdevice well adapted for use in this application. In these sifters, threescreens are used and the top surface of each screen is contacted byrotatable arms that extend radially from the center of the sifter. Thearms have a V shaped cross section so as to force the powder into aconverging space between the arm and the screen as the arm rotates tothereby force a controlled volume of powder through the screen. Asensing system based on the height of organic material 160 in firstcontainer 50 (or on an integrated signal derived from the depositionrate and time of operation) can serve to actuate the devices agitatingscreens 110 and 120 so as to maintain a nearly constant volume of powderin first container 50. Agitating devices such as piezoelectricstructures 140 prevent the buildup of organic material in the feed pathto first container 50. Piezoelectric structures can be vibrated withmultiple frequencies, e.g. a siren effect, to prevent the buildup oforganic material at vibrational nodes.

Maintaining a nearly constant volume of organic material 160 in firstcontainer 50 promotes a constant feed rate of powder in auger structure80. The feed rate uniformity is further improved when the powder inproximity to the infeed portion of the screw auger is maintained in afluidized state by an agitating device. This can be accomplished byslowly agitating the powder immediately above the auger screw or byinducing vibration, e.g. by piezoelectric structure 130, into the powderthat is tuned to induce liquid-like behavior of the powder but is not soenergetic as to cause gas-like behavior.

Turning now to FIG. 4, there is shown in further detail across-sectional view of one embodiment of a portion of the aboveapparatus for feeding and vaporizing powder according to the presentinvention. Auger structure 80 transfers organic material powder alongfeeding path 60 into manifold 20 and heating element 170. Heatingelement 170 can be e.g. a heated screen and has been previouslydescribed in detail by Long et al. Manifold 20 includes a vaporizationzone which is defined as the region of feeding path 60 immediatelyadjacent to heating element 170. A thin cross-section of organicmaterial powder is heated to the desired rate-dependent temperature,which is the temperature of heating element 170, by virtue of contactand thermal conduction, whereby the thin cross-section of organicmaterial powder vaporizes to be delivered to a substrate surface to forma layer. The auger structure 80 and its rotation rate control the rateat which organic material is fed to heating element 170. This linearlycontrols the rate of vaporization and therefore the rate at whichorganic material leaves the manifold in the vapor state. Thus the feedrate of the organic material to the auger structure and to thevaporization zone controls the deposition rate of the vaporized organicmaterial onto the desired surface.

Additionally, base 180 can be included. Base 180 is a heat-dissipatingstructure to prevent much of the heat from heating element 170 fromtraversing the length of feeding path 60, and thus keeps the bulk of theorganic material significantly cooler than the conditions it experiencesin the vaporization zone immediately adjacent to heating element 170.Means of heat dissipation for base 180 have been described by Long etal. in commonly-assigned, above-cited U.S. patent application Ser. No.10/784,585. A steep thermal gradient thereby created protects all butthe immediately vaporizing material from the high temperatures. Thevaporized organic vapors rapidly pass through heating element 170 andcan enter into the heated manifold 20. The residence time of organicmaterial at the desired vaporization temperature is very short and as aresult, thermal degradation is greatly reduced. The residence time ofthe organic material at elevated temperature, that is, at therate-dependent vaporization temperature, is orders of magnitude lessthan prior art devices and methods (seconds vs. hours or days in theprior art), which permits heating organic material to highertemperatures than in the prior art. Thus, the current device and methodcan achieve substantially higher vaporization rates, without causingappreciable degradation of the organic material components.

The organic material can include a single component, or can include twoor more different organic material components, each one having adifferent vaporization temperature. The vaporization temperature can bedetermined by various means. For example, FIG. 5 shows a graphicalrepresentation of vapor pressure versus temperature for two organicmaterials commonly used in OLED devices. The vaporization rate isproportional to the vapor pressure, so for a desired vaporization rate,the data in FIG. 5 can be used to define the required heatingtemperature corresponding to the desired vaporization rate. In the casewhere the organic material includes two or more organic components, thetemperature of heating element 170 is chosen such that the vaporizationis feed-rate limited, that is, the vapor pressure at the heating elementtemperature is substantially above the desired partial pressure of thatcomponent in the manifold, so that each of the organic materialcomponents simultaneously vaporizes.

Pressure develops in manifold 20 as vaporization proceeds, and streamsof vapor exit manifold 20 through the series of apertures 30 shown inFIG. 2. Because only a small portion of organic material—the portionresident in the vaporization zone—is heated to the rate-dependentvaporization temperature, while the bulk of the material is kept wellbelow the vaporization temperature, it is possible to interrupt thevaporization by a means for interrupting heating at heating element 170,e.g. stopping the movement of auger structure 80. This can be done whena substrate surface is not being coated so as to conserve organicmaterial and minimize contamination of any associated apparatus, such asthe walls of a deposition chamber, which will be described below.

Because heating element 170 can be a fine mesh screen that preventspowder or compacted material from passing freely through it, themanifold can be used in any orientation. For example, manifold 20 ofFIG. 2 can be oriented down so as to coat a substrate placed below it.This is an advantage not found in the heating boats of the prior art.

Turning now to FIG. 6 a, there is shown a cross-sectional view of oneembodiment of an auger structure useful in this invention. The augerstructure 80 includes an auger screw 85 that is turned by motor 90. Thedistance between the threads of the screw helix and the thread heightare chosen to be sufficiently large that powder tends not to pack intoand rotate with the helix, but rather to remain at the bottom of ahorizontally oriented auger tube and be transported linearly by virtueof the relative motion between the screw and the auger tube. Forexample, an auger screw with a 2.5 mm pitch screw lead and a 0.8 mmthread height has been found to be an effective combination intransporting and consolidating organic material powders in a horizontalorientation.

In the horizontal orientation, the organic material travels along thebottom of auger screw 85 in a tumbling and dispersed form. At theterminal end of auger screw 85, a powder pressure of 1 Mpa can bedeveloped that increases the bulk density of the organic material to thepoint where it serves as a vapor seal, preventing vaporized material inthe manifold having a pressure greater than the ambient vacuum levelfrom flowing back along the auger screw to the powder source container.As shown in FIG. 6 b, the terminal end of auger screw 85 is configuredto have a thread-free portion 135 having a constant circular crosssection over a small length to constrain the consolidated powder to forma narrow annular or tubular shape. This narrow annular shapesubstantially improves the thermal contact and temperature uniformitythrough the organic material, between the temperature-controlled augerscrew 85 and the temperature-controlled feeding path 60. Thisconfiguration additionally assures good temperature uniformity of theorganic material at a given transverse cross section relative to acircular cross section and substantially increases the attainabletemperature gradient in the organic material between the auger structureand the heating element. The powder is extruded from the auger structurein a tubular shape and is sufficiently consolidated that it can maintainthe tubular extruded form for at least several millimeters upon exitingthe support of the auger tube. This solid form prevents pressurizedvapor, resulting from organic material vaporization, from flowing backinto the auger structure and enables the powder to bridge the short gapbetween the end of the temperature-controlled auger structure and theheating element.

Thermal modeling of a powder dispensing system having this annularconfiguration where the heating element is spaced 130 μm from the end ofthe auger structure indicates that an average axial thermal gradient of0.5° C./μm can be achieved through the organic material spanning theheating element and the terminal end of the auger structure when thetemperature differential between the two is 270° C. There can thereforebe a 100° C. temperature drop through the first 200 μm of consolidatedpowder. This gradient prevents the usual leaching of more volatileconstituents from bulk volumes of mixed-component organic materials andenables a single source to co-deposit multiple organic materials. Thislarge gradient is further instrumental in maintaining the organicmaterial in a consolidated powder form at the exit of the auger tubeeven when organic materials that liquefy before vaporizing are employed.

The auger structure shown in FIG. 6 a is effective at transportingorganic material powders horizontally, but is not as effective intransporting organic material powders vertically, since the powder tendsto simply rotate with the screw and not advance along the length of thestructure. Turning now to FIG. 6 c, there is a relief view of anotherembodiment of an auger structure useful in this invention. In thisembodiment, auger structure 95 includes two or more auger screws, e.g.auger screws 85 a, 85 b, and 85 c, with identical interlaced helicalthreads. All of the auger screws 85 a, 85 b, and 85 c rotate in the samedirection. Organic material that is packed between the threads of oneauger screw, e.g. 85 a, will be removed as the material rotates intocontact with the interlaced thread of the second rotating auger screw,e.g. 85 b, because the facing portions of adjacent screws move inopposite directions. Auger structure 95 thus overcomes the orientationrestrictions of the single-screw auger structure of FIG. 6 a whileretaining the ability to consolidate the powder into a solid shape andform a vapor seal. The discharge portion of auger structure 95 wouldhave an elongated cross-section that can extend across the entire lengthof the manifold so as to inject material substantially uniformly alongits length.

Turning now to FIG. 6 d, there is a cross-sectional view of anotherembodiment of an auger structure useful in this invention. Augerstructure 105 includes a rotating helical thread 115, a stationarycenter portion 125, and a stationary outer tube, which in this case isfeeding path 60. In this embodiment, only a portion of auger structure105—the portion comprising helical threads 115—rotates and is turned bymotor 90. Powder feeding with circular cross section helical threads hasbeen demonstrated. The thread consisted of a steel wire 0.7 mm diameterformed into a helix of 5 mm outside diameter and 2.5 mm pitch. Smoothwires of other materials such as titanium and stainless steel are alsosuitable. The wire can also have a non-circular cross section, with arectangular cross section being particularly advantageous as it providesadditional rigidity to prevent the helical thread from changingdimensions as it encounters torsional resistance while pushing thepowder. Stationary center portion 125, in cooperation with feeding path60, substantially prevents all but a thin film of organic material fromrotating with the auger. Auger structure 105 does not rely on gravity toaccumulate organic material powder and will operate in any orientation.Auger structure 105 also consolidates the organic material into a thinannular shape that substantially improves the thermal contact betweenthe organic material and temperature-controlled feeding path 60 andstationary center portion 125. These characteristics are significant inenabling the controlled vaporization of mixed component organicmaterials, and organic materials that liquefy before vaporizing. Thusthis embodiment overcomes the orientation restrictions of the firstauger structure while retaining the ability to consolidate the powderinto a solid shape and form a vapor seal.

The above embodiments of this invention, based primarily on vaporizationapparatus 10 of FIG. 2, are useful at atmospheric pressure and pressuresdown to about one-half atmosphere. Experimentally, it has been observedthat fine powder is considerably more difficult to meter in a partialvacuum below half an atmosphere. The powder agglomerates as residual airmolecules are removed, and undergoes a reduction of the elastic couplingbetween particles that is effective in communicating vibrational energythrough powder under atmospheric conditions. This effect negativelyinfluences the powder-feeding uniformity of the auger structure.Therefore, a different agitating device can be necessary. Turning now toFIG. 7, there is shown a cutaway view of another embodiment of anagitating device useful in the present invention for overcoming thelimitations in low-pressure conditions. This embodiment employs threepiezoelectric structures as the agitating device. Piezoelectricstructures 150 and 155 are inclined at a steep angle and form oppositewalls of a funnel at the bottom of first container 50. The bottomportion 190 of these two piezoelectric structures is not supported andleads directly to the infeed portion of auger structure 80. Theunsupported portions of the piezoelectric structures have high vibrationamplitude and are effective in fluidizing powder in proximity to theirsurfaces. The third piezoelectric structure 130 is mounted below augerstructure 80 and imparts vibration whose amplitude is essentiallyperpendicular to the vibration of the other two piezoelectricstructures. The piezoelectric structures are driven by a frequencysweeping circuit. The changing frequency is instrumental in preventingthe formation of nodes and improves the powder feeding efficiencyconsiderably. Auger structure 80 can be any of the above-described augerstructures.

FIG. 8 is a cutaway view of another embodiment of an agitating deviceuseful in the present invention for overcoming the limitations inlow-pressure conditions. Opening 230 represents the lower end of theabove-described first container 50. Rotating thread type device 210includes left- and right-hand helically wound wires on a common shaft.Rotating thread type device 210 is positioned above the infeed portionof the auger structure such that the wires are substantially tangent tothe threads of auger structure 80. The rotating thread should notinterfere with the auger screw threads, but it will continue to operateeffectively with as much as 1 mm clearance. Rotating thread type device210 is slowly rotated via gear drive 220, by motor 90, which also turnsauger structure 80. In practice, the rotational speed of the rotatingthread type device 210 can vary depending on the particle size andproperties of the particular powder, but a practical guide is to havethe axial slew rate of the rotating thread match the axial slew rate ofthe threads of the auger screw. The wires of rotating thread type device210 tend to push organic material toward the center of opening 230 andprevent powder bridging over auger structure 80. Auger structure 80 canbe any of the above-described auger structures. This agitating device iswell adapted to feeding mixed-component organic materials as it impartsvery little energy to the powder and is therefore not likely to causeparticle separation by size or density.

Turning now to FIG. 9, there is shown a three-dimensional view of aportion of another embodiment of an apparatus according to the presentinvention for vaporizing organic materials and condensing them onto asurface to form a layer, including an apparatus to drive off adsorbedgasses or impurities. The apparatus includes first container 50 asdescribed above for holding a quantity of organic material. Theapparatus can also include a second container 70 for holding a reservequantity of organic material that can be fed to first container 50. Theapparatus can also include agitating devices such as piezoelectricstructure 140 to facilitate the movement of organic material from secondcontainer 70 to first container 50. Organic material from firstcontainer 50 is fed into first feeding path 260. First feeding path 260includes an auger structure in association with first container 50 fortransferring the organic material from first container 50 to firstfeeding path 260. At least a portion of the auger structure is turned bymotor 240 to feed organic material powder along first feeding path 260.First feeding path 260 includes vacuum exposure opening 270, which is incommunication with a source of partial vacuum. First feeding path 260can be heated so as to heat the organic material while exposing it to apartial vacuum so as to drive off adsorbed gasses or impurities as theorganic material is transferred along first feeding path 260 to thevaporization zone. For typical deposition rates, the free powder hasseveral minutes to liberate adsorbed water vapor and gas molecules justprior to being compacted and vaporized. The organic material is thentransferred to second feeding path 265, which is defined by an augerstructure as described above, in which it is consolidated, that is, itis compacted and evenly distributed around the auger structure. Organicmaterial powder is fed along second feeding path 265 by the augerstructure to a manifold and vaporization zone (not shown) as describedabove, where the organic material is vaporized and subsequentlycondensed onto the surface of an OLED substrate to form an organiclayer. Optional third container 250 can receive the exposed organicpowder from first feeding path 260. In such a case, the auger structurethat defines second feeding path 265 is also associated with thirdcontainer 250 for feeding exposed powder to second feeding path 265, andsuch auger structure passes through the interior of third container 250.This apparatus also includes means for fluidizing the organic materialpowder, as already described. In an alternative embodiment, feeding path260 includes vacuum exposure opening 270 and feeds directly to amanifold without the use of a second feeding path.

In practice, the apparatus described herein is operated as follows. Anorganic material, which is useful in forming a layer on an OLED device,is provided into second container 70. The organic material istransferred in a controlled manner to first container 50 in such a wayas to maintain a substantially constant volume of organic material infirst container 50. The organic material is fluidized by means describedherein and thereby transferred to an auger structure 80, which transfersthe organic material to a vaporization zone as described herein. Theorganic material is vaporized in the vaporization zone into a manifold20, which delivers the vaporized organic material to the surface of anOLED substrate to form a layer, as will be described below.

Turning now to FIG. 10, there is shown an embodiment of a device of thisdisclosure including a deposition chamber enclosing a substrate.Deposition chamber 280 is an enclosed apparatus that permits an OLEDsubstrate 285 to be coated with organic material transferred frommanifold 20. Manifold 20 is supplied with organic material via feedingpath 60 as described above. Deposition chamber 280 is held undercontrolled conditions, e.g. a pressure of 1 torr or less provided byvacuum source 300. Deposition chamber 280 includes load lock 275 whichcan be used to load uncoated OLED substrates 285, and unload coated OLEDsubstrates. OLED substrate 285 can be moved by translational apparatus295 to provide even coating of vaporized organic material over theentire surface of OLED substrate 285. Although vaporization apparatus isshown as partially enclosed by deposition chamber 280, it will beunderstood that other arrangements are possible, including arrangementswherein the entire vaporization apparatus, including any container orcontainers for holding the organic material powder, is enclosed bydeposition chamber 280.

In practice, an OLED substrate 285 is placed in deposition chamber 280via load lock 275 and held by translational apparatus 295 or associatedapparatus. The vaporization apparatus is operated as described above,and translational apparatus 295 moves OLED substrate 285 perpendicularto the direction of emission of organic material vapors from manifold20, thus delivering vaporized organic material to the surface of OLEDsubstrate 285 to condense and form a layer of organic material on thesurface.

Turning now to FIG. 11, there is shown a cross-sectional view of a pixelof a light-emitting OLED device 310 that can be prepared in partaccording to the present invention. The OLED device 310 includes at aminimum a substrate 320, a cathode 390, an anode 330 spaced from cathode390, and a light-emitting layer 350. The OLED device can also include ahole-injecting layer 335, a hole-transporting layer 340, anelectron-transporting layer 355, and an electron-injecting layer 360.Hole-injecting layer 335, hole-transporting layer 340, light-emittinglayer 350, electron-transporting layer 355, and electron-injecting layer360 include a series of organic layers 370 disposed between anode 330and cathode 390. Organic layers 370 are the organic material layers mostdesirably deposited by the device and method of this invention. Thesecomponents will be described in more detail.

Substrate 320 can be an organic solid, an inorganic solid, or acombination of organic and inorganic solids. Substrate 320 can be rigidor flexible and can be processed as separate individual pieces, such assheets or wafers, or as a continuous roll. Typical substrate materialsinclude glass, plastic, metal, ceramic, semiconductor, metal oxide,semiconductor oxide, semiconductor nitride, or combinations thereof.Substrate 320 can be a homogeneous mixture of materials, a composite ofmaterials, or multiple layers of materials. Substrate 320 can be an OLEDsubstrate, that is a substrate commonly used for preparing OLED devices,e.g. active-matrix low-temperature polysilicon or amorphous-silicon TFTsubstrate. The substrate 320 can either be light transmissive or opaque,depending on the intended direction of light emission. The lighttransmissive property is desirable for viewing the EL emission throughthe substrate. Transparent glass or plastic are commonly employed insuch cases. For applications where the EL emission is viewed through thetop electrode, the transmissive characteristic of the bottom support isimmaterial, and therefore can be light transmissive, light absorbing orlight reflective. Substrates for use in this case include, but are notlimited to, glass, plastic, semiconductor materials, ceramics, andcircuit board materials, or any others commonly used in the formation ofOLED devices, which can be either passive-matrix devices oractive-matrix devices.

An electrode is formed over substrate 320 and is most commonlyconfigured as an anode 330. When EL emission is viewed through thesubstrate 320, anode 330 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials useful in this invention are indium-tin oxide and tin oxide,but other metal oxides can work including, but not limited to, aluminum-or indium-doped zinc oxide, magnesium-indium oxide, and nickel-tungstenoxide. In addition to these oxides, metal nitrides such as galliumnitride, metal selenides such as zinc selenide, and metal sulfides suchas zinc sulfide, can be used as an anode material. For applicationswhere EL emission is viewed through the top electrode, the transmissivecharacteristics of the anode material are immaterial and any conductivematerial can be used, transparent, opaque or reflective. Exampleconductors for this application include, but are not limited to, gold,iridium, molybdenum, palladium, and platinum. The preferred anodematerials, transmissive or otherwise, have a work function of 4.1 eV orgreater. Desired anode materials can be deposited by any suitable meanssuch as evaporation, sputtering, chemical vapor deposition, orelectrochemical means. Anode materials can be patterned using well knownphotolithographic processes.

While not always necessary, it is often useful that a hole-injectinglayer 335 be formed over anode 330 in an organic light-emitting display.The hole-injecting material can serve to improve the film formationproperty of subsequent organic layers and to facilitate injection ofholes into the hole-transporting layer. Suitable materials for use inhole-injecting layer 335 include, but are not limited to, porphyriniccompounds as described in U.S. Pat. No. 4,720,432, plasma-depositedfluorocarbon polymers as described in U.S. Pat. No. 6,208,075, andinorganic oxides including vanadium oxide (VOx), molybdenum oxide(MoOx), nickel oxide (NiOx), etc. Alternative hole-injecting materialsreportedly useful in organic EL devices are described in EP 0 891 121 A1and EP 1 029 909 A1.

While not always necessary, it is often useful that a hole-transportinglayer 340 be formed and disposed over anode 330. Desiredhole-transporting materials can be deposited by any suitable means suchas evaporation, sputtering, chemical vapor deposition, electrochemicalmeans, thermal transfer, or laser thermal transfer from a donormaterial, and can be deposited by the device and method describedherein. Hole-transporting materials useful in hole-transporting layer340 are well known to include compounds such as an aromatic tertiaryamine, where the latter is understood to be a compound containing atleast one trivalent nitrogen atom that is bonded only to carbon atoms,at least one of which is a member of an aromatic ring. In one form thearomatic tertiary amine can be an arylamine, such as a monoarylamine,diarylamine, triarylamine, or a polymeric arylamine. Exemplary monomerictriarylamines are illustrated by Klupfel et al. in U.S. Pat. No.3,180,730. Other suitable triarylamines substituted with one or morevinyl radicals and/or comprising at least one active hydrogen-containinggroup are disclosed by Brantley et al. in U.S. Pat. Nos. 3,567,450 and3,658,520.

A more preferred class of aromatic tertiary amines are those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include thoserepresented by structural Formula A.

wherein:

-   -   Q₁ and Q₂ are independently selected aromatic tertiary amine        moieties; and    -   G is a linking group such as an arylene, cycloalkylene, or        alkylene group of a carbon to carbon bond.

In one embodiment, at least one of Q1 or Q2 contains a polycyclic fusedring structure, e.g., a naphthalene. When G is an aryl group, it isconveniently a phenylene, biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural Formula A andcontaining two triarylamine moieties is represented by structuralFormula B.

where:

-   -   R₁ and R₂ each independently represent a hydrogen atom, an aryl        group, or an alkyl group or R₁ and R₂ together represent the        atoms completing a cycloalkyl group; and    -   R₃ and R₄ each independently represent an aryl group, which is        in turn substituted with a diaryl substituted amino group, as        indicated by structural Formula C.

wherein R₅ and R₆ are independently selected aryl groups. In oneembodiment, at least one of R₅ or R₆ contains a polycyclic fused ringstructure, e.g., a naphthalene.

Another class of aromatic tertiary amines are the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by Formula C, linked through an arylene group. Usefultetraaryldiamines include those represented by Formula D.

wherein:

-   -   each Are is an independently selected arylene group, such as a        phenylene or anthracene moiety;    -   n is an integer of from 1 to 4; and    -   Ar, R₇, R₈, and R₉ are independently selected aryl groups.

In a typical embodiment, at least one of Ar, R₇, R₈, and R₉ is apolycyclic fused ring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural Formulae A, B, C, D, can each in turn be substituted. Typicalsubstituents include alkyl groups, alkoxy groups, aryl groups, aryloxygroups, and halogens such as fluoride, chloride, and bromide. Thevarious alkyl and alkylene moieties typically contain from 1 to about 6carbon atoms. The cycloalkyl moieties can contain from 3 to about 10carbon atoms, but typically contain five, six, or seven carbonatoms—e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures.The aryl and arylene moieties are usually phenyl and phenylene moieties.

The hole-transporting layer in an OLED device can be formed of a singleor a mixture of aromatic tertiary amine compounds. Specifically, one canemploy a triarylamine, such as a triarylamine satisfying the Formula B,in combination with a tetraaryldiamine, such as indicated by Formula D.When a triarylamine is employed in combination with a tetraaryldiamine,the latter is positioned as a layer interposed between the triarylamineand the electron-injecting and transporting layer. The device and methoddescribed herein can be used to deposit single- or multi-componentlayers, and can be used to squentially deposit multiple layers.

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. In addition, polymerichole-transporting materials can be used such as poly(N-vinylcarbazole)(PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such aspoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also calledPEDOT/PSS.

Light-emitting layer 350 produces light in response to hole-electronrecombination. Light-emitting layer 350 is commonly disposed overhole-transporting layer 340. Desired organic light-emitting materialscan be deposited by any suitable means such as evaporation, sputtering,chemical vapor deposition, electrochemical means, or radiation thermaltransfer from a donor material, and can be deposited by the device andmethod described herein. Useful organic light-emitting materials arewell known. As more fully described in U.S. Pat. Nos. 4,769,292 and5,935,721, the light-emitting layers of the organic EL element include aluminescent or fluorescent material where electroluminescence isproduced as a result of electron-hole pair recombination in this region.The light-emitting layers can include a single material, but morecommonly include a host material doped with a guest compound or dopantwhere light emission comes primarily from the dopant. The dopant isselected to produce color light having a particular spectrum. The hostmaterials in the light-emitting layers can be an electron-transportingmaterial, as defined below, a hole-transporting material, as definedabove, or another material that supports hole-electron recombination.The dopant is usually chosen from highly fluorescent dyes, butphosphorescent compounds, e.g., transition metal complexes as describedin WO 98/55561, WO 00/18851, WO 00/57676, and WO 00/70655 are alsouseful. Dopants are typically coated as 0.01 to 10% by weight into thehost material. The device and method described herein can be used tocoat multi-component guest/host layers without the need for multiplevaporization sources.

Host and emitting molecules known to be of use include, but are notlimited to, those disclosed in U.S. Pat. Nos. 4,768,292; 5,141,671;5,150,006; 5,151,629; 5,294,870; 5,405,709; 5,484,922; 5,593,788;5,645,948; 5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721; and6,020,078.

Metal complexes of 8-hydroxyquinoline and similar derivatives (FormulaE) constitute one class of useful host materials capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 500 nm, e.g., green, yellow, orange, and red.

wherein:

-   -   M represents a metal;    -   n is an integer of from 1 to 3; and    -   Z independently in each occurrence represents the atoms        completing a nucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be a monovalent,divalent, or trivalent metal. The metal can, for example, be an alkalimetal, such as lithium, sodium, or potassium; an alkaline earth metal,such as magnesium or calcium; or an earth metal, such as boron oraluminum. Generally any monovalent, divalent, or trivalent metal knownto be a useful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

The host material in light-emitting layer 350 can be an anthracenederivative having hydrocarbon or substituted hydrocarbon substituents atthe 9 and 10 positions. For example, derivatives of9,10-di-(2-naphthyl)anthracene constitute one class of useful hostmaterials capable of supporting electroluminescence, and areparticularly suitable for light emission of wavelengths longer than 400nm, e.g., blue, green, yellow, orange or red.

Benzazole derivatives constitute another class of useful host materialscapable of supporting electroluminescence, and are particularly suitablefor light emission of wavelengths longer than 400 nm, e.g., blue, green,yellow, orange or red. An example of a useful benzazole is 2, 2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole].

Desirable fluorescent dopants include perylene or derivatives ofperylene, derivatives of anthracene, tetracene, xanthene, rubrene,coumarin, rhodamine, quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyrilium and thiapyriliumcompounds, derivatives of distryrylbenzene or distyrylbiphenyl,bis(azinyl)methane boron complex compounds, and carbostyryl compounds.

Other organic emissive materials can be polymeric substances, e.g.polyphenylenevinylene derivatives, dialkoxy-polyphenylenevinylenes,poly-paraphenylene derivatives, and polyfluorene derivatives, as taughtby Wolk et al. in commonly assigned U.S. Pat. No. 6,194,119 B1 andreferences cited therein.

While not always necessary, it is often useful that OLED device 310includes an electron-transporting layer 355 disposed over light-emittinglayer 350. Desired electron-transporting materials can be deposited byany suitable means such as evaporation, sputtering, chemical vapordeposition, electrochemical means, thermal transfer, or laser thermaltransfer from a donor material, and can be deposited by the device andmethod described herein. Preferred electron-transporting materials foruse in electron-transporting layer 355 are metal chelated oxinoidcompounds, including chelates of oxine itself (also commonly referred toas 8-quinolinol or 8-hydroxyquinoline). Such compounds help to injectand transport electrons and exhibit both high levels of performance andare readily fabricated in the form of thin films. Exemplary ofcontemplated oxinoid compounds are those satisfying structural FormulaE, previously described.

Other electron-transporting materials include various butadienederivatives as disclosed in U.S. Pat. No. 4,356,429 and variousheterocyclic optical brighteners as described in U.S. Pat. No.4,539,507. Benzazoles satisfying structural Formula G are also usefulelectron-transporting materials.

Other electron-transporting materials can be polymeric substances, e.g.polyphenylenevinylene derivatives, poly-para-phenylene derivatives,polyfluorene derivatives, polythiophenes, polyacetylenes, and otherconductive polymeric organic materials such as those listed in Handbookof Conductive Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., JohnWiley and Sons, Chichester (1997).

An electron-injecting layer 360 can also be present between the cathodeand the electron-transporting layer. Examples of electron-injectingmaterials include alkaline or alkaline earth metals, alkali halidesalts, such as LiF mentioned above, or alkaline or alkaline earth metaldoped organic layers.

Cathode 390 is formed over the electron-transporting layer 355 or overlight-emitting layer 350 if an electron-transporting layer is not used.When light emission is through the anode 330, the cathode material caninclude nearly any conductive material. Desirable materials have goodfilm-forming properties to ensure good contact with the underlyingorganic layer, promote electron injection at low voltage, and have goodstability. Useful cathode materials often contain a low work functionmetal (<3.0 eV) or metal alloy. One preferred cathode material iscomprised of a Mg:Ag alloy wherein the percentage of silver is in therange of 1 to 20%, as described in U.S. Pat. No. 4,885,221. Anothersuitable class of cathode materials includes bilayers comprised of athin layer of a low work function metal or metal salt capped with athicker layer of conductive metal. One such cathode is comprised of athin layer of LiF followed by a thicker layer of Al as described in U.S.Pat. No. 5,677,572. Other useful cathode materials include, but are notlimited to, those disclosed in U.S. Pat. Nos. 5,059,861; 5,059,862; and6,140,763.

When light emission is viewed through cathode 390, it must betransparent or nearly transparent. For such applications, metals must bethin or one must use transparent conductive oxides, or a combination ofthese materials. Optically transparent cathodes have been described inmore detail in U.S. Pat. No. 5,776,623. Cathode materials can bedeposited by evaporation, sputtering, or chemical vapor deposition. Whenneeded, patterning can be achieved through many well known methodsincluding, but not limited to, through-mask deposition, integral shadowmasking as described in U.S. Pat. No. 5,276,380 and EP 0 732 868, laserablation, and selective chemical vapor deposition.

Cathode materials can be deposited by evaporation, sputtering, orchemical vapor deposition. When needed, patterning can be achievedthrough many well known methods including, but not limited to,through-mask deposition, integral shadow masking as described in U.S.Pat. No. 5,276,380 and EP 0 732 868, laser ablation, and selectivechemical vapor deposition.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   5 vaporization device-   6 source-   7 source-   8 source-   9 vapor plume-   10 vaporization apparatus-   15 substrate-   20 manifold-   30 aperture-   40 feeding apparatus-   50 first container-   60 feeding path-   70 second container-   80 auger structure-   85 auger screw-   85 a auger screw-   85 b auger screw-   85 c auger screw-   90 motor-   95 auger structure-   100 organic material-   105 auger structure-   110 screen-   115 helical thread-   120 screen-   125 center portion-   130 piezoelectric structure-   135 thread-free portion-   140 piezoelectric structure-   150 piezoelectric structure-   155 piezoelectric structure-   160 organic material-   170 heating element-   180 base-   190 bottom portion-   210 rotating thread type device-   220 gear driver-   230 opening-   240 motor-   250 third container-   260 first feeding path-   265 second feeding path-   270 vacuum exposure opening-   275 load lock-   280 deposition chamber-   285 OLED substrate-   295 translational apparatus-   300 vacuum source-   310 OLED device-   320 substrate-   330 anode-   335 hole-injecting layer-   340 hole-transporting layer-   350 light-emitting layer-   355 electron-transporting layer-   360 electron-injecting layer-   370 organic layers-   390 cathode

1. A method for forming an OLED device comprising: a) providing asubstrate and a first electrode over the substrate; b) forming a firstorganic layer over the first electrode by: i) providing firstparticulate organic material in a first feeding path; and ii)mechanically transferring material consisting of the first particulateorganic material along the first feeding path to a first vaporizationzone using an auger structure, wherein the first vaporization zone ismaintained at a constant temperature and the feed rate of the firstparticulate organic material to the first vaporization zone controls thedeposition rate of the first vaporized organic particulate material; andc) forming a second electrode over the first organic layer.
 2. Themethod of claim 1 wherein the first organic layer is a light emittinglayer.
 3. The method of claim 2 wherein the first particulate organicmaterial includes at least a host material and a dopant material.
 4. Themethod of claim 1 wherein the temperature of the first particulateorganic material in the first feeding path is maintained below thedesired vaporization temperature.
 5. The method of claim 1 furtherincluding metering, at a controlled volumetric rate or pressure, thefirst particulate organic into the vaporization zone.
 6. The method ofclaim 1 further comprising d) before forming the second electrode,forming a second organic layer over the first electrode by: i) providingsecond particulate organic material in a second feeding path; and ii)mechanically transferring organic material consisting of the particulatematerial along the second feeding path to a second vaporization zoneusing an auger structure, wherein the second vaporization zone ismaintained at a constant temperature and the feed rate of theparticulate organic material to the second vaporization zone controlsthe deposition rate of the second vaporized organic particulatematerial.
 7. The method of claim 6 wherein the second organic layer isan electron-transport layer, an electron-injecting layer, ahole-transport layer or a hole-injecting layer.
 8. The method of claim 1further including selecting the first feeding path orientation andproviding an auger structure along such first feeding path.
 9. Themethod of claim 8 wherein mechanically transferring the firstparticulate organic material comprises rotating at least a portion ofthe auger structure.
 10. The method of claim 9 wherein the augerstructure extrudes the first particulate organic material in a solidform.
 11. The method of claim 10 wherein the solid fonn has a tubularshape that is maintained after exiting the auger structure.
 12. Themethod of claim 10 where in the solid form acts as a vapor sealpreventing pressurized vapor from flowing back into the auger structure.13. The method of claim 8 wherein the first feeding path orientation ishorizontal.